1. Field of the Invention
The present invention relates to a vehicle air conditioner having a variable displacement compressor that is driven at least by a vehicle engine. The vehicle air conditioner performs air-conditioning of a passenger compartment by controlling the discharge capacity of the variable displacement compressor from an outside based on a cooling load of the passenger compartment.
2. Description of Related Art
In a vehicle air conditioner described in U.S. Pat. No. 5,867,996 (corresponding to JP-A-10-236151), a variable displacement compressor is driven by a vehicle engine when a cooling load of the vehicle air conditioner is larger than a predetermined value. Further, when the cooling load of the vehicle air conditioner is lower than the predetermined value, the variable displacement compressor is driven by an electric motor. However, in this vehicle air conditioner, the displacement (discharge capacity) of the variable displacement compressor is controlled based on the cooling load. Therefore, after the cooling load becomes higher than the predetermined value, the displacement is increased slowly in accordance with the cooling load. As a result, a long time is necessary until the cooling load becomes lower than the predetermined value. In this case, the variable displacement compressor needs to be driven by the vehicle engine for the long time, so fuel consumption efficiency of the vehicle engine is deteriorated.